The disclosure relates to a device for guiding electromagnetic radiation with an optical fibre, wherein the fibre is introduced into a projection exposure apparatus for semiconductor lithography.
Projection exposure apparatuses for semiconductor lithography contain, inter alia, optical elements for optically influencing the EUV or VUV radiation used for imaging. In order to improve the optical ray guiding and the optical imaging performance, the optical elements can in part also be heated, for example in order to homogenize a temperature distribution across the relevant optical element and thus to prevent undesired, temperature-induced deformations of the optical element. By way of example, electromagnetic infrared radiation (for short: IR radiation) can be used for heating the optical elements. In this case, the IR radiation impinges on the optical element, is partly absorbed there and heats said element as a consequence. It can be advantageous to guide the electromagnetic radiation using an optical fibre from the outside into the EUV projection exposure apparatus, the infrared radiation source being situated outside the EUV projection exposure apparatus. The waste heat from the light source can thus be dissipated separately and an additional, undesired energy input into the EUV projection exposure apparatus by the waste heat from the light source is avoided by the use of the fibre. By way of example, a fibre-coupled laser that emits infrared radiation can be used as a radiation source. The optical fibre proceeding from the laser is generally embodied as a single-mode fibre. In order to transport high radiation powers from the output of the light source fibre to the location of the optical element to be heated, a further optical fibre, e.g. a multimode fibre, is used.
At the exit end of the optical fibre that leads to the optical element in the projection exposure apparatus, an inhomogeneous intensity profile distribution of the electromagnetic radiation can be present. Given a lack of homogeneity, rotational symmetry of the radiation distribution with respect to the centre of the fibre cross section is not present. In particular, cases can occur in which the centroid of the intensity profile distribution is situated eccentrically with respect to the fibre cross section. These inhomogeneous distributions of the electromagnetic radiation at the exit end of the fibre have the disadvantage that there impinges on the optical elements in the projection exposure apparatus an electromagnetic radiation which results in an undesired heating of the optical element on account of an incorrect spatially resolved distribution. A correct heating of the optical elements is facilitated, in particular, when the intensity profile distribution at the exit end of the fibre is homogeneous.